1. Field of the Invention
The present invention relates generally to high stiffness parabolic structures and, more specifically to high stiffness parabolic structures utilizing integral reinforcing grids.
2. Description of the Prior Art
Many spacecraft applications require rigid, low-weight, and thermally stable components. Specifically, current spacecraft antenna applications require high precision reflector contours (RMS 0.010 to 0.0005 inch), low weight, low thermal distortion and therefore, feature a variety of configurations requiring lightweight, thermally stable composite materials. Conventional methods for the fabrication of spacecraft antenna employ the use of a bonded facesheet-to-honeycomb core sandwich construction. The facesheet-to-honeycomb core sandwich construction typically uses a composite facesheet and an aluminum honeycomb core. Space applications which employ the sandwich construct, and experience the extremes of thermal fluctuations, have components which are subject to stress due to the thermal expansion mismatch between the facesheet and core. Further, space applications for reflectors are extremely weight sensitive and therefore, any savings in weight over that present in the typical heavy honeycomb construct is highly desirable.
In addition to thermal expansion mismatch and weight considerations, the facesheet-to-honeycomb sandwich construction has a core of constant thickness measured perpendicular to the reflector surface and, as the honeycomb core becomes Thicker relative to the curvature of the paraboloid, the back surface facesheet gets distinctly different from the front surface facesheet. The result is a front facesheet which is generally parabolic in shape and a back facesheet which is non-parabolic in shape. The difference in shape between the front and back facesheets requires each facesheet to be fabricated with different specifications.
While various designs, like that disclosed in U.S. Pat. No. 3,940,891, have been used to satisfy high rigidity, low weight requirements for space application components and structures which are flat or singly curved in shape, applications related to parabolic antenna reflectors and similar doubly curved structures have not been addressed.
Based on techniques known in the art for the construction of antenna reflectors and similarly doubly curved structures, a composite isogrid structure for parabolic surfaces is highly desirable.